In a leading-edge advanced system LSI (Large Scale Integration), along with the progress of element miniaturization, there arises a problem of increase in wiring delay (RC (Resistance-Capacitance) delay) which is proportional to a product of a wiring resistance and a wiring parasitic capacity. As a countermeasure against this problem, the wiring resistance is reduced by the use of a copper (Cu) wiring and also there has been frequently employed a method of reducing the parasitic capacity by using an insulating film having a relative permittivity k not lower than 2.5 and not higher than 3.1 (low-k film) as an interlayer insulating film. Recently, as a material having further lower relative permittivity, there has been developed a porous low-k film obtained by introducing vacancies in a low-k film, and the like.
Patent Document 1 (Japanese Patent Laid-Open No. 2010-182946) describes that a plurality of wiring trenches is formed in a film which includes an insulating film of a low vacancy rate region having a low vacancy rate and an insulating film of a high vacancy rate region having a vacancy rate higher than the low vacancy rate region, and a Cu wiring is formed in each of the wiring trenches. Here, it is described that, in the insulating film between the respective wirings, an insulating film of a low vacancy rate region is formed in a peripheral part of a side wall in each of the wiring trenches, and a region having a relatively high vacancy density is formed in a region of the insulating film except the peripheral region of the side wall in each of the wiring trenches.
Patent Document 2 (Japanese Patent Laid-Open No. 2010-171072 and Patent Document 3 (Japanese Patent Laid-Open No. 2011-109036) describe that the vacancy occupation rate per a unit volume in an insulating film is changed in the film thickness direction by increase of a porogen flow rate during a film formation process of the insulating film. Patent Document 3 describes that a vacancy diameter increases particularly in the center part of the insulating film in the film thickness direction.